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Abstract:

The present invention relates to surgical instruments particularly
suitable for preparing vertebral endplates during spinal inter-body
surgical procedures. Methods of using such instruments are also
disclosed.

Claims:

1. A method of performing spinal surgery comprising the steps of: (a)
obtaining a surgical instrument having a longitudinal axis, a transverse
axis orthogonal to the longitudinal axis, top and bottom surfaces each
with rasp teeth, a first portion, and a second portion, wherein the first
portion and the second portion are longitudinally offset from each other,
a section of the proximal end of the first portion is connected to a
section of the distal end of the second portion, the first portion is
generally D-shaped in a transverse cross-section, the second portion has
a generally rectangular-shaped body and includes an access portion
extending parallel to the longitudinal axis of the instrument and
extending through the body of the second portion, and the first portion
and the second portion each have a substantially equivalent width along
the transverse axis of the surgical instrument; (b) exposing the spine
and identifying the center of at least one target vertebral disc; (c)
removing the anterior annulus of the at least one vertebral disc and
performing at least a partial discectomy, thus creating at least one
inter-vertebral cavity; (d) removing a sufficient amount of spinal
endplate cartilage to expose underlying bone; (e) distracting at least
one inter-vertebral cavity; (f) using the first portion of the surgical
instrument to prepare at least one of the posterior-lateral and
anterior-lateral regions of one or more spinal endplates; and (g)
providing a reamer through the access portion of the second portion of
the surgical instrument to further prepare the one or more spinal
endplates.

2. The method of claim 1, wherein the step (b) of exposing the spine
comprises an anterior surgical approach.

3. The method of claim 1, wherein a complete discectomy is performed.

4. The method of claim 1, wherein the step (f) of lateral preparation of
one or more spinal endplates comprises the step of contra-laterally
rotating the surgical instrument.

5. The method of claim 1, wherein the step (g) of providing a reamer
includes fluoroscopic guidance.

6. The method of claim 1 further comprising the step of placing an
appropriately sized implant into the prepared inter-vertebral cavity.

7. A method of performing spinal surgery comprising the steps of: (a)
obtaining a surgical instrument having a longitudinal axis and a first
portion connectable with a second portion, the first portion including
top and bottom surfaces with rasp teeth, the second portion including an
access portion extending parallel to the longitudinal axis of the
surgical instrument and extending through the second portion; (b)
exposing the spine and identifying the center of at least one target
vertebral disc; (c) removing the anterior annulus of the at least one
vertebral disc and performing a discectomy, thus creating an
inter-vertebral cavity; (d) removing a sufficient amount of spinal
endplate cartilage to expose underlying bone; (e) distracting the
inter-vertebral cavity; (f) using the first portion of the surgical
instrument to prepare at least one of the posterior-lateral and
anterior-lateral regions of one or more spinal endplates on a first side;
(g) passing a reamer through the access portion of the surgical
instrument to further prepare the one or more spinal endplates on the
first side; (h) removing the surgical instrument from the disc space; (i)
flipping the surgical instrument 180 degrees about the longitudinal axis
of the access portion and reamer; (j) removing the reamer from the
surgical instrument and using the first portion of the surgical
instrument to prepare at least one of the posterior-lateral and
anterior-lateral regions of one or more spinal endplates on a second
side, contra-lateral to the first side; and (k) passing the reamer
through the access portion of the surgical instrument to further prepare
the one or more spinal endplates on the second side.

8. The method of claim 7, wherein the step of exposing the spine
comprises an anterior surgical approach.

9. The method of claim 7, wherein at least one of the steps (g) and (k)
of passing the reamer includes fluoroscopic guidance.

10. The method of claim 7 further comprising the step of placing an
appropriately sized implant into the prepared inter-vertebral cavity.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.
12/137,760, filed on Jun. 12, 2008 and issued as U.S. Pat. No. 7,947,044,
which is a continuation of application Ser. No. 10/973,481, filed on Oct.
26, 2004, and now abandoned. The entire disclosure of these earlier
applications is expressly incorporated by reference herein.

FIELD OF THE INVENTION

[0002] This invention relates to surgical instruments and methods of using
such instruments. The instruments are particularly suitable for preparing
vertebral endplates during spinal inter-body implant procedures.

BACKGROUND OF THE INVENTION

[0003] In the simplest terms, the spine is a column made of vertebrae and
discs. The vertebrae provide the support and structure of the spine while
the spinal discs, located between the vertebrae, act like cushions or
"shock absorbers." These discs also contribute to the flexibility and
motion of the spinal column. Over time, the discs may become diseased,
infected, develop deformities such as tears/cracks, or simply lose
structural integrity, for example, bulge or flatten. These impaired discs
can affect the anatomical functions of the vertebrae, due to the
resultant lack of proper biomechanical support, and are often associated
with chronic back pain. Chronic back pain afflicts a large percentage of
the world's population and often interferes with one's ability to
participate in regular daily activities.

[0004] Several surgical techniques have been developed to address spinal
defects, such as disc degeneration and/or deformity. Spinal fusion has
become a recognized surgical procedure for restoring biomechanical and
anatomical integrity to the spine. Spinal fusion techniques involve the
removal, or partial removal, of at least one inter-vertebral disc and
preparation of the disc space for receiving an implant by shaping the
exposed vertebral endplates. An implant is then inserted between the
opposing endplates. Vertebral endplates can have complex shapes due to
various anatomical and biological factors. For example, a vertebral
endplate may be concave in some portions. The vertebral endplates may
also have surface irregularities and even bony protuberances, or
osteophytes, which can be difficult to remove. These osteophytes, found
predominately about the posterior-lateral portions of the endplate, are
especially problematic as they can painfully impinge on nearby anatomical
structures and reduce the useable implant-seating surface to primarily
the medial-anterior portion of the disc space. This reduction in seating
area may compromise biomechanical integrity by reducing the area in which
to distribute mechanical forces, thus increasing the apparent stress
experienced by both the implant and vertebral endplate.

[0005] Proper endplate preparation is important to successful spinal
fusion surgery procedures. To achieve fusion, it is generally necessary
to expose bleeding endplate bone stock. This initiates the biological
healing process of the bone and encourages implant integration. The
surgeon must also conform or shape the endplate to, at least, approximate
the implant geometry thereby ensuring proper seating of the spinal
implant in the disc space. One of the many challenges of preparing the
endplates is the discrepancy between the shape of the endplates and the
implant. While the spinal endplates may have a complex surface
topography, the mating surfaces of spinal implants are generally flat.
Thus, the surgeon may initially desire to provide the maximum surface
area for proper implant seating by simply razing enough endplate bone
stock to ensure a relatively flat surface.

[0006] In addition to maximizing the surface area available for implant
seating, the surgeon should also preserve as much surface vertebral
endplate bone as possible by minimizing the amount of bone removed since
this subchondral bone is generally much stronger than the underlying
cancellous bone. Preservation of the endplate bone stock ensures
biomechanical integrity of the endplates and minimizes the risk of
implant subsidence. Thus, the surgeon should provide for optimal seating
of the implant while still maximizing the amount of available securing
endplate bone stock.

[0007] The surgeon may rely on a number of instruments during complex
spinal surgical procedures. With the advent of spinal fusion surgery and
the development of spinal implants, there is an increasing need for
complimentary instruments. These complimentary instruments should reduce
the "instrument load" on the surgeon while increasing the efficiency and
precision of the surgical procedure. These instruments should also
compliment the final size and shape of the implant to be used, again
increasing the efficiency of the surgical procedure, while decreasing the
overall need for multiple instruments. While there are many instruments
that may be required for such complex spinal surgical procedures, there
is a need in the art for a single instrument suitable for preparing
vertebral endplates to properly receive a spinal implant for spinal
surgery procedures.

[0008] Methods of endplate preparation have traditionally been performed
"by-hand" using a variety of instruments. Traditional free-hand
instruments such as box chisels, osteotomes, curettes, drills, milling
instruments and the like, which aid in shaping the endplate, also
aggressively, and sometimes unevenly, remove bone. Even when used by the
most skilled surgeons, these traditional free-hand instruments may prove
difficult to control in order to achieve uniform and reproducible results
during endplate preparation. The surgeon must also avoid damaging nearby
anatomical structures, such as the spinal cord or vertebral arteries.
These previously known "by-hand" methods and instruments are generally
cumbersome, lack precision, and may lead to the removal of excessive
amounts of vertebral endplate bone stock.

[0009] None of these approaches provide a single multi-purpose surgical
instrument, as is now taught, for allowing controlled and precise
preparation of vertebral endplates while preserving endplate bone stock.
Thus, there is a need in the art for a single spinal surgical instrument
which reduces the instrument load and the number of operating steps for a
surgeon, improves visualization of the disc space while minimizing
exposure of the disc space, and improves surgical safety by increasing
the precision of complimentary free-hand instruments while reducing the
risk of damage to nearby anatomical structures.

[0010] There is a further need in the art for an instrument for the
improved preparation of spinal endplates, especially one which can be
used to prepare the posterior-lateral regions of the endplates and/or the
entire endplate. There is also a need for a single instrument that can be
flipped about its longitudinal axis outside of the disc space, and
re-inserted to address features of both the left and right
posterior-lateral regions of a vertebral endplate. For example, a single
multi-purpose instrument should be capable of preparing both the lateral
and contra-lateral sides of a vertebral endplate. Still further there is
a need for a single instrument capable of preparing both the left and
right posterior-lateral regions of vertebral endplates and for removing
osteophytes.

BRIEF SUMMARY OF THE INVENTION

[0011] The present invention is directed to surgical instruments and
methods of using such instruments. The instruments are particularly
suitable in spinal surgeries for preparing a vertebral endplate during an
anterior approach procedure.

[0012] Certain preferred embodiments of the present invention provide for
precise and controlled preparation of vertebral endplates using free-hand
surgical instruments. Certain preferred embodiments of the present
invention also provide for improved safety in addressing features of the
vertebral endplate posterior-lateral regions, including the removal of
posterior-lateral osteophytes. Still other preferred embodiments allow
for improved visualization of the disc space during surgical procedures
while minimizing exposure of the operating space.

[0013] Certain embodiments of the present invention include a surgical
instrument having both a rasp and a guide body. The instrument has a
generally D-shaped first portion which is longitudinally offset from, and
connected to, a generally rectangular shaped second portion. The first
portion serves as a rasp, while the second portion includes an access
port that serves as a device guide. As used herein, a device for use in
accordance with certain embodiments of the present invention may be,
without limitation, any free-hand instruments including a reamer, box
chisel, osteotome, curette, drill, milling instrument or the like, which
aid in preparing vertebral endplates. The second portion may also include
any number of housings or structures capable of guiding a device such as,
for example and without limitation, through-holes, access ports, frames,
carriages, tracks, etc. Still further, the device may be controllably
advanced along the longitudinal axis of the second portion. The second
portion may further include a threaded opening for attachment to a
threaded holder.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1A shows a perspective view of an embodiment of one surgical
instrument of the invention (10) having a generally D-shaped first
portion (20) and a second portion (30). FIG. 1B further depicts a top
view of the same embodiment. Lastly, FIG. 1C depicts a side view of the
embodiment showing a transverse aperture (50) of the D-shaped portion
(20).

[0015] FIG. 2A is a perspective view of an embodiment of the surgical
instrument (10) having a contact member (90). FIG. 2B further depicts an
embodiment having a contact member only on the upper surface, while FIG.
2C depicts contact members (90) on both the upper and lower surfaces.

[0016] FIG. 3A depicts a top view of an embodiment of the surgical
instrument (10) configured to accept a reamer (200) though a device guide
(80). FIG. 3B depicts a side view of the surgical instrument (10) showing
visualization of the reamer through the transverse aperture (50).

[0017] FIG. 4 illustrates a perspective view of an embodiment of the
surgical instrument (10) configured to accept a box chisel (300).

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0018] Certain presently preferred aspects of the present invention may be
used for the preparation of spinal endplates for a variety of inter-body
implant procedures. These procedures include, but are not limited to,
spinal fusion, vertebral body replacement, and artificial disc
procedures. Thus, certain embodiments of the present invention are
directed to an instrument and method for use in spinal surgery
procedures. Certain embodiments of the surgical instrument are
particularly suitable for procedures in which an implant is placed
between adjacent vertebrae, such as in spinal fusion procedures, or those
which use an implant to replace all or part of one or more vertebral
bodies such as during vertebral body replacement procedures. For either
procedure, stability of the implant is a major concern, thus implant
loosening and/or motion should be avoided as either condition may impair
implant performance, result in anatomical damage, present substantial
pain to the patient, and may result in implant expulsion from the disc
space. As such, proper preparation of the disc space and, particularly,
the spinal endplates is critical.

[0019] In accordance with certain embodiments of the present invention, a
surgical instrument is provided comprising both a rasp and a device
guide. As shown in FIG. 1, the instrument (10) includes a generally
D-shaped first portion (20) which is longitudinally offset from, and
connected to, a generally rectangular shaped second portion (30). The
posterior-lateral-most aspect of the first portion (20) is rounded such
that its contour matches the posterior-lateral aspects of the inter-body
implant for good conformity. Both the top and bottom surfaces of the
first portion include a rasp (40) for endplate preparation.
Alternatively, first portion (20) may have a rasp (40) on either the top
or bottom surfaces. Rasp (40) may cover any degree of the top and/or
bottom surfaces, but preferably covers the entire top and bottom surface
of the first portion. The first portion (20) also includes an aperture
(50) that extends the entire transverse length of the first portion (20),
thus the first portion may be predominantly hollow. Alternatively, first
portion 20 may include a plurality of apertures (50) having a uniform or
varied size/shape. These apertures (50) aid in the fluoroscopic
visualization of a device, such as a reamer (200), during a surgical
procedure as either an embodiment of the surgical instrument of the
present invention or a reamer is advanced into the disc space. The second
portion (30) includes a threaded opening (60) on the most proximal end
surface, or front face, (70) for attachment to a threaded holder (not
shown). The second portion (30) also includes an access port that serves
as a device guide (80) adjacent the threaded opening (60). Device guide
(80) is particularly useful for controlling the trajectory of free-hand
devices, thus increasing the precision of the surgical procedure while
also providing for controlled removal of bone in the posterior-lateral
regions. First portion (20) may be substantially planar or substantially
cylindrical. First portion (20) may also act as a stabilizing element in
reducing vibration, and other unwanted movement, while improving
free-hand instrument balance and precision. First portion (20), including
rasp portion (40), may further serve as a standard rasp for initial
preparation and roughening of the vertebral endplate surface with minimal
bone removal. The surgeon may therefore choose to skip an initial rasping
step using a standard free-hand rasp, and may instead use certain
embodiments of the present invention for rasping as well as targeted bone
removal. The first portion and/or second portion may also have at least
one graded marking or measurement, to gauge the depth of penetration into
the disc space.

[0020] Certain embodiments of the present invention may also include at
least one raised shoulder or contact member (90). The contact members may
be any variety of sizes or shapes, so designed to abut at least one
adjacent vertebral body. The contact members may also be slidably and/or
rotatably connected to second portion (40). Still further, contact member
(90) may be extendable to abut a plurality of adjacent vertebrae, as
needed. Contact member (90) may be particularly useful in preventing or
minimizing damage to nearby anatomical structures.

[0021] Preferred embodiments of the present invention are particularly
suited for shaping the lateral aspects of the posterior portion of the
endplate. The instruments of the present invention can be used with a
variety of implants. In particular, those implants having a generally
annular shape with rounded corners, for example elliptical or "D" shaped,
may be used in accordance with the present invention. In still other
preferred embodiments of the present invention device guide (80) may be
used with a reamer. In use, a reamer (200) is inserted through the device
guide (80) and used to precisely shape the lateral aspects of the
posterior portion of the endplate to match the corresponding geometry of
the implant. The reamer also aids in the removal of posterior osteophytes
and may be provided with a depth control feature such as a collet or
shoulder to prevent the reamer from breaching the disc space and damaging
nearby anatomical structures. For the remainder of the endplate
preparation, the rasp portion (40) of the instrument (10) is used. Thus,
the present invention allows easy and precise reaming of the lateral
corners of the posterior endplate, while at the same time provides a rasp
for preparing the remainder of the endplate. The instrument can be
flipped 180 degrees about the longitudinal axis of device guide (80) (an
imaginary line which runs orthogonal to the front face (70) of the
instrument (10) to the distal end of the instrument and would run
parallel to the longitudinal centerline of an inserted reamer device). In
this manner, the instrument can first be used to prepare the left side of
the endplate, removed from the disc space, rotated 180 degrees, and
re-inserted to the disc space to prepare the right side of the endplate.
This "flipping" action is particularly convenient in cases where there
are posterior-lateral osteophytes which require removal prior to
preparing the disc space. Thus, certain preferred embodiments of the
present invention can be flipped to remove osteophytes on both sides of
the endplate, then used to properly ream and prepare the disc space.

[0022] In certain embodiments of the present invention, the second portion
(30) may also include a threaded opening (60) on the most proximal end
surface, or front face, (70) for attachment to a threaded holder (not
shown). Still further, second portion (30) may be removably attached to a
holder by a variety of engagement structures including, but not limited
to, interlocking components or snug-fit mating components. In other
embodiments, the present invention is integral with a holder (not shown).
And yet in other embodiments, the first portion (20), second portion
(30), and holder are all modular components that are assembled during
surgery.

[0023] In still other embodiments of the present invention, second portion
may also include any number of housings or structures capable of guiding
a device such as, for example and without limitation, through-holes,
access ports, frames, carriages, tracks, etc. Embodiments of device guide
(80) may be any number of shapes including circular, rectangular,
irregular, or custom shaped to a particular device. Still further, the
device may be controllably advanced along the longitudinal axis of the
second portion. The second portion may further have any number of
mechanisms or structures which facilitate controllable device advancement
therefrom. For example, and without limitation, the second portion (30)
may contain a threaded access port (80) to accept a threaded reamer; a
track, carriage or frame that may be controllably extended from the
second portion; an access port (80) having an internal ratchet or other
stop-motion mechanism operatively engaged with a reamer; and/or a
telescoping access port (80). Thus, second portion (30) may provide for
controlled reamer (200) advancement, and controlled reaming depth, into
the disc space. Controlled depth of reaming may be particularly useful in
preventing, minimizing or even eliminating damage to the surrounding
anatomical structures. An alternate embodiment of the present instrument
may be configured for use with a free-hand box chisel, or similar
instrument. In this manner, access port (80) of second portion (30)
serves as a device guide for improved safety, uniformity, and precision
of a chisel device.

[0024] Embodiments of the present surgical instrument are preferably made
of a durable material such as stainless steel, stainless steel alloy,
titanium, or titanium alloy, but can also be made of other durable
materials such as, but not limited to, polymeric, ceramic or composite
materials. Durable materials may also consist of any number of pure
metals and/or metal alloys. Certain embodiments of the present invention
may also include more than one material. For example, the first portion
may be made of a metal alloy and the second portion may be made of a
ceramic material.

[0025] Certain preferred embodiments of the present invention may include
a rasp portion (40) of various sizes. In certain embodiments of the
invention, modular rasp portion (40) may be provided in varying sizes,
shapes, and/or degrees of coarseness, which may be connected to the
remaining modular components during surgery. For example, first portions
(20) of various size, etc. may be removably connectable to a single base
second portion (30), or alternatively may be assembled to various second
portions (30). In yet still another embodiment, there may be multiples,
or a series, of instruments (10) each having a rasp portion (40) of
various sizes, or shapes and/or degrees of coarseness, which are made
available during surgery. Still further, rasp portion (40) may act as a
spacer to maintain a desired intradiscal height while the lateral aspects
of the endplates are prepared to a desired shape using a reamer or other
suitable tool. Thus, the entire spinal endplate final geometry can be
conveniently prepared to match a desired implant geometry for optimal
seating of the implant in the disc space.

[0026] Different sizes of rasp portion (40) may cover various percentages
of the available medial-lateral disc space. For example, one embodiment
of rasp portion (40) may cover the entire medial-lateral width of the
disc space. Other embodiments of rasp portion (40) may cover 50%, or more
of the medial-lateral width of the disc space with the remainder of the
instrument serving as a guide for a reamer designed particularly for
preparation of the spinal endplate, including removal of
posterior-lateral osteophytes in the disc space. In yet another
embodiment of the present invention, the entire width of the instrument
is equivalent to the entire width of the implant to be inserted.

EXAMPLE

[0027] A certain embodiment of the present invention was used to prepare
spinal endplates to receive a vertebral body replacement. In this
surgical procedure, the spine was first exposed via an anterior approach
and the center of the target disc was identified. The anterior annulus
was then removed and a complete discectomy was performed. Residual
cartilage was removed from the spinal endplates to expose bleeding bone.
The resultant disc space was distracted by impacting sequentially larger
heights of distractors/trial spacers into the disc space, until a tight
feel was obtained.

[0028] Spinal endplate preparation started with a standard general rasp
which was impacted into the disc space for initial coarse rasping and
then removed. A size-specific rasp-reamer guide instrument (10) of the
present invention was then used to remove strong osteophytes in the
posterior-lateral region of the spinal endplate. The size specific
rasp-reamer guide instrument (10) was impacted into the disc space via
the end face of an optional instrument holder connected via opening (60).

[0029] A size-specific reamer (200) was advanced through the opening (80)
of size specific rasp-reamer guide instrument (10), under fluoroscopic
guidance, to remove posterior osteophytes on one side. A size-specific
reamer (200) and rasp-reamer guide instrument (10) were then removed from
the disc space. The rasp-reamer guide instrument (10) was then flipped
about 180 degrees about the longitudinal axis of reamer guide (80), and
the previously discussed steps were repeated for the contra-lateral side
of the spinal endplate.

[0030] After adequately preparing the endplates, the appropriately sized
implant was selected, packed with graft material and placed in the
prepared disc space.

[0031] Those skilled in the art will appreciate that numerous changes and
modifications can be made to the many embodiments of the invention and
that such changes and modifications can be made without departing from
the spirit of the invention. It is therefore intended that the appended
claims cover all such equivalent variations as falling within the true
spirit and scope of the invention.